Did Facebook pay just $83M for that giant pile of IBM patents?

News today that Facebook is spending$550 million to buy 650 patents held by Microsoft came just weeks after it made what seemed to be an even bigger purchase from IBM in which it spent an undisclosed sum to acquire 750 patents.

It looks like those IBM patents are not nearly as valuable to Facebook as the ones once held by AOL that the social network bought from Microsoft today.

In Facebook's amended S-1, which it filed today with the Security and Exchange Commission, Facebook said that in the first quarter it spent $83 million acquiring patents. The updated S-1 talks about today's Microsoft deal but doesn't mention the IBM transaction, which happened on March 22.

A patent's value varies, of course, but patent experts had reasoned that the price tag would be higher than $83 million, which comes out to about $111,000 per patent. The patents Facebook bought from IBM are said to cover a broad range of "software and networking" technology.

Facebook declined to comment.

The social network, which ended 2011 with just 56 patents, has been bulking up its intellectual property portfolio in advance of its initial public offering. It started its purchasing spree after Yahoo filed a suit in March claiming that Facebook was infringing on 10 Yahoo patents. There was speculation that Facebook would quickly countersue and then settle, or perhaps even buy a chunk of Yahoo's patent portfolio outright to make the problem go away.

Facebook did countersue, claiming Yahoo is infringing on 10 of Facebook's patents, but a speedy settlement looks less and less likely. Instead, it has been buying up patents from other companies, largely to help it with its battle with Yahoo and to protect itself against others that might be looking to file a Yahoo-like suit, especially once Facebook's pockets (presumably) become even deeper after its IPO.

All told, based on information in its S-1 and today's deal with Microsoft, Facebook now has 1,424 patents and almost 550 filed patent applications.